How to revive a sourdough starter you forgot in the fridge

A forgotten starter is usually asleep, not dead

PJ Hamel, writing on the King Arthur Baking blog, puts it bluntly: it is very difficult to kill a sourdough starter, especially through benign neglect. Forgetting to feed it, in her words, just means it is taking a very long nap. The University of Illinois Extension agrees that starters are highly resilient and can more than likely be revived.

That resilience has limits. Illinois explains that the longer a starter goes without food, the higher its acidity climbs, and that too much acid makes it hard for the beneficial bacteria to survive. That is why a starter left for a week bounces back quickly while one left for months needs patience. King Arthur's maintenance guide says a starter forgotten in the back of the refrigerator for months can probably still be brought back, but it may take nearly as long as creating a new one from scratch.

What a neglected starter looks like

The most common sight is liquid on top. Illinois explains that the yeasts produce alcohol along with carbon dioxide, and when a starter hasn't been fed in a while that alcohol collects as a dark liquid that bakers call hooch. Colorado State University Extension says a liquid layer that smells of alcohol is fine and can be poured off or stirred in. The University of Alaska Fairbanks Cooperative Extension says the same about liquid that separates after a starter stands for several days: stir it in and feed it.

Hamel describes how the jar changes with time in the fridge. After a week there is usually a thin layer of clear to light-amber liquid. After a month the hooch has darkened, which she reads as the starter having ramped down its activity. After several months it can be almost black, or dried into a dark gray, corrugated skin; she peels the skin off and finds very hungry, cream-colored starter underneath. Colorado State adds that a refrigerated starter that isn't fed regularly may grow whitish clumps on the surface of the liquid, which it identifies as yeasts rather than mold.

A step-by-step revival routine

Deal with the liquid. Stir it back in or pour it off. Hamel says either works, though stirring in dark hooch may turn the starter a little gray for a while.
Keep a small portion and feed it. Following King Arthur Baking's method, measure out 50 grams, about a quarter cup, and discard the rest. Feed the 50 grams with 50 grams of unbleached all-purpose flour and 50 grams of water. Because the starter has been in the fridge, she uses warm, not hot, tap water to help it along.
Give it 12 warm hours. Let it rest at room temperature for 12 hours. King Arthur calls 75 to 78°F ideal; a cooler room only means a slower wake-up. A rubber band around the jar at the starting level, and another at double that height, makes any rise easy to read.
Check, then repeat. Any rise or any bubbles mean it is alive. If nothing has changed, discard and feed the same way again and check after another 12 hours. Keep going until it doubles within 12 hours, and before baking bread without added commercial yeast, until it doubles within six to eight hours of a feeding.

How long recovery takes

Time depends mostly on how long the starter was ignored. In Hamel's own test, a neglected starter showed no activity after its first feeding and 12-hour rest, then nearly doubled within five hours of its second feeding. Bringing a starter fully back to its normal self, she writes, might take another couple of feedings or several days' worth. King Arthur's maintenance guide gives the general rule: a starter that missed a day, a week or two weeks of feedings can almost certainly be revived by feeding it every 12 hours until it is healthy, then returning it to its regular schedule.

The University of Illinois Extension's advice for monthly bakers fits the same pattern: take the starter out of the fridge the day before you bake and expect to feed it a couple of times 12 hours apart to get it going. Colorado State University Extension notes that rehydrating a dried starter likewise takes several days of regular feeding before it bubbles, rises and smells pleasantly sour.

If progress stalls, look at warmth and flour before giving up. Illinois suggests moving a sluggish starter somewhere warmer or switching to rye flour, and names 70 to 82°F as the range where yeast stays active. For a starter that has dried into a chalky block, Hamel's limit is three or four days of daily feedings with no growth and no bubbles; after that she suggests starting over and stirring some of the old starter into the new one.

When a starter should not be revived

Revival is for a hungry starter, not a contaminated one, and extension services describe the difference in similar terms. Colorado State University Extension says a starter showing any sign of mold, colored or fuzzy, should not be used, and that the container should be thoroughly cleaned before starting over. South Dakota State University Extension describes a starter that has gone bad in terms of mold growing in and on it, a noticeable foul smell, and discoloration such as green, pink or orange spots. Illinois says to discard the starter if mold appears.

King Arthur draws the line the same way: color in the starter itself, beyond the cream and amber of hooch, anywhere in the pink, blue, green or orange range means throwing it out, as does a smell that is genuinely off rather than just strongly of alcohol or vinegar.

This guide covers feeding a neglected starter back to activity. It does not judge whether a particular starter is safe to eat. If you are unsure, follow the food-safety guidance from your local cooperative extension service.

Common revival mistakes

Reviving the whole jar. Feeding everything that is left multiplies the volume at every step. Keeping a small portion, as Hamel does with 50 grams, makes each feeding a large meal relative to the starter and keeps the jar manageable. It also sends the oldest starter to the bin, which she says you probably won't want to bake with anyway.

Quitting after one feeding. A starter that has sat for weeks often shows nothing after the first 12 hours; Hamel's example only woke up after its second feeding. Keeping it cold. A revival in a chilly kitchen still works, just slowly, because fermentation slows at colder temperatures, as Colorado State notes.

Losing count of the feedings. A revival is a run of feedings 12 hours apart, which is easy to lose track of. Doughmi, a sourdough starter care app, never lets a starter die in the app: after three full rhythms without food its face turns a little droopy, and a Start again button logs the revival feeding with a Fresh start badge and resets its reminder from that moment.

Frequently asked questions

Is the dark liquid on top of my sourdough starter bad?

A dark liquid layer is what bakers call hooch, alcohol made by the yeast when a starter has gone a while without food. The University of Illinois Extension says to pour it off or stir it in, and Colorado State University Extension says a liquid layer that smells of alcohol is fine. Colored spots or fuzz in the starter itself are a different matter, covered above.

How long can a sourdough starter sit in the fridge and still be revived?

Sources give no fixed cutoff. King Arthur Baking says a starter forgotten for months can probably still be brought back, though it can take nearly as long as making a new one, and its blog shows a starter neglected for at least six months with healthy-looking starter under a dried skin. The University of Illinois Extension cautions that acidity keeps rising the longer a starter goes unfed.

Can I bake with the starter I discard during revival?

King Arthur Baking suggests not keeping the first discard, since a neglected starter is probably old enough that you won't want to bake with it. Discard from later feedings, once the starter is active again, can go into discard recipes.